The present invention relates generally to a system and method for controlling an ignition timing of an internal combustion engine, and in particular relates to the system and method therefor, wherein the ignition timing is controlled so that a correction of the ignition timing angle value is quickly made during an engine transient operating condition.
A conventional engine ignition timing system described above is exemplified by Japanese Patent Application Unexamined Open No. Sho. 59-39,974 published on Mar. 5, 1984. In the disclosed system, pressure in a combustion chamber of the engine (cylinder pressure) is detected, a mean value .theta.pmax is calculated from each value of detected crankshaft rotational angles .theta.pmax at which pressure in a particular engine cylinder or an arbitrary number of the engine cylinders has reached its maximum per compression stroke N times (for example, about 20 times), and the ignition timing is then corrected according to a comparison result between the mean value .theta.pmax and a target value at which an engine output torque is a maximum (generally from 10 degrees after the top dead center (10.degree. ATDC) to 15 degrees after the top dead center (15.degree. ATCD)). This control mode is called MBT control (Minimum spark advance for Best Torque control).
However, since, in the above-identified system, the mean value .theta.pmax is not calculated until the detected cranksaft rotational angle values .theta.pmax are measured, e.g., 20 times for each combustion stroke, the ignition timing is corrected actually once for each time that 20 values of the maximum crank angle values .theta.pmax are accumulated. Consequently, the correction of the ignition timing for MBT is delayed so that driveability of the engine is reduced when, e.g., the engine is operated under a transient (acceleration/deceleration) state.